Conventionally, as a portable printer, there is provided a thermal printer on which a thermal head having a plurality of heating elements arranged in the width direction of paper to be printed is mounted. The thermal printer is generally driven by battery power. In the case of the printing operation by a thermal printer described in Jpn. Pat. Appln. publication of patent applications No. 2007-30263, which is a patent document of a Japanese patent application, various information items can be printed by activating those of the plural heating elements which correspond to portions to be printed.
In the portable printer, paper is fed to a setting position of the thermal head by driving a platen roller set to face the thermal head by use of a pulse motor.
However, the temperature of the pulse motor rises when the pulse motor is continuously operated. If the pulse motor is continuously used and the temperature of the pulse motor becomes a preset temperature or higher, there occurs a problem that the pulse motor may be broken.
In order to prevent the occurrence of breakage due to a temperature rise, in some printers the operation of the pulse motor is controlled, by use of a temperature sensor, so as to keep the temperature of the pulse motor lower than a preset temperature. However, since the temperature sensor is expensive, a problem that the printer cannot be realized at low cost occurs.